Modern tornado outlooks still start with colored pencil drawings

Meteorologists have an unprecedented array of high-tech equipment at their disposal, from supercomputers that crunch millions of physics equations to Doppler radar arrays that can scan individual thunderstorms in three dimensions. Yet each day, many weather forecasters begin their shifts the same way their meteorological predecessors did decades ago: by putting pencil to paper and mapping the current state of the weather.

This method of manual weather analysis is especially popular at the National Oceanic and Atmospheric Administration's (NOAA) Storm Prediction Center in Norman, Oklahoma.

This center, known simply as "SPC" in the weather world, is responsible for issuing severe thunderstorm and tornado watches for the entire U.S., which means that its forecasters must have a solid grasp of small-scale weather features that could trigger individual thunderstorms to form. Forecasters at SPC have been especially busy during the past few days, with severe thunderstorms, many of them unleashing large hail, erupting from Texas to Virginia.

One storm on Thursday night produced a massive "wedge" tornado that struck the small town of Fairdale, Illinois, causing major damage. (The SPC had issued a tornado watch, and a local National Weather Service office issued a tornado warning, that covered this storm.)

Greg Carbin, SPC's warning coordination meteorologist, says the process of manually analyzing current weather is "fading" from widespread use, but it's key to making a successful weather forecast.

"If you don't have a decent idea as to why the atmosphere is doing something in its current state," he told Mashable in an interview, "how do you expect you’re going to forecast?"

He says penciling in lines of equal temperature, air pressure, moisture content, and upper air features such as jet stream winds — each with a different shade of colored pencil — amount to "a method of diagnosis before you move into prognosis."

"I often try on a shift to not even look at any guidance before I've looked at as much observational info as I can," he says, referring to computer models.

Carbin says the computer models take a lot of the small-scale subtleties of the weather out, instead making assumptions or smoothing over small-scale perturbations on the scale of a county or city-level. However, when it comes to severe thunderstorms — SPC's bread and butter — the small-scale features, such as a small kink in a warm front, can mean the difference between a life-saving forecast and a severe weather outbreak that catches people off guard.

"So much of what drives severe weather is on the small scale," Carbin says. He progresses on to more high-tech forecasting methods, using computer models and other tools, after finishing the pencil and paper analysis.

According to him, not every meteorologist believes that a good forecast starts with a hand-drawn map.

"You can skate by, especially if you're dealing with large-scale weather systems and maximum and minimum temperature and precipitation forecasts for the next few days."

"But if you’re involved in mesoscale forecasting like we are here," he warns, "I just don’t think you’re going to succeed... without that hands-on approach to incorporating, assimilating” large amounts of data onto the page.

Carbin says his SPC colleagues are true believers in the hand-drawn maps. "The majority of forecasters here believe in that approach and find it extremely valuable and useful." Oftentimes, these maps alone can provide a forecaster with a feel for whether a day may turn out to produce violent storms, or fizzle out with just garden variety pop-up showers.

For all their value, though, the hand-drawn maps are akin to prescriptions written by physicians — they can be impossible for others to read. Instead, they're what Carbin calls "a personal endeavor."

"I can’t get a lot out of someone else's hand analysis," he says.

Another aspect of the hand-drawn maps is that, though they are meant to describe the present, once they're completed, the atmosphere has already moved ahead several steps.

"The minute you think it's figured out, it's already changed," Carbin says. "You're already looking at the past by the time you’re finished."

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